Noise from furnace mounted in the crawlspace

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Posted by: from Carlisle
1/27/2022 at 12:22:19 PM

This past summer, we had a new furnace and AC installed in the crawlspace, located directly under the master bedroom. Like the previous furnace, the new furnace was installed horizontally. However, this time it was mounted to the floor joists (see pic). The previous furnace was on a platform that was resting on the ground.

Everything was okay with the new AC, but once the cooler weather rolled in, we noticed the new furnace was really loud, much louder than the previous furnace.

The property is up north and is a short-term rental. Every guest we've had this winter has mentioned or complained about the noise. I was up there last week and can confirm the noise is way too much, especially when trying to sleep.

I contacted the contractor that installed the system, and he said there was nothing he could do and suggested we insulate the crawlspace ceiling with safe and sound, so I had someone come by to quote me on the job ($1800 for 240 sq/ft). The guy said that the insulation would help, but he also thinks a lot of the noise is from the furnace mounted to the floor joists, causing vibration, so the insulation might not give us the desired outcome.

Will the safe n sound help enough with the noise? Is there a noise-dampening device used for these types of floor joist-mounted installs, and if so, should they have been added by the contractor that installed the furnace? Is there anything else we can do?

In addition to the constant noise of the furnace, there is a loud BANG coming from the ductwork below the bedroom each time the furnace fan shuts down. It seems like it's from the metal contracting when there's no longer any air pressure. Like the furnace noise, the bang was not a problem with the previous furnace. I checked online and some suggested making sure all the vents were open. We did this, but it hasn't helped. We can avoid the duct bang noise by keeping the furnace fan running, but that means there is constant noise in the bedroom from the fan.

We're going nuts trying to get this figured out, so any help you can provide would be greatly appreciated!

Noise from furnace mounted in the crawlspace
Noise from furnace mounted in the crawlspace
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Date/Time1/27/2022 at 5:20:29 PM

Hi Gerald,

Unfortunately there are many reasons that the noise is happening vibration through floor, fan on too high of a speed, improper gas pressure in system, wrong ac coil, just to name a few. As for the loud bang it could also be many things improper sized duct, duct not manufactured correctly, too much air resistance in duct system, furnace too big.

Without seeing and or hearing it it would be hard to diagnose. How far up north is the property amd is it something you d like a second opinion on? If you like to give me a call I can try to narrow it down over the phone with you or I could make a site visit, depending n location.

Unfortunately many installers put in a new furnace the same size as the old one without properly sizing the system based on new technologies. I also find that many installers start the furnace without a proper commissioning procedure.

Feel free to call me if he happy to help if I can.


Chris Walsh

Breathe Rite Mechanical


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Richard in Edmonton
Date/Time1/27/2022 at 7:45:26 PM

I suspect there will be no satisfactory solution without substantial alteration/reinstallation of the system, likely including supporting the furnace from the bottom as before. As the previous respondent has suggested there could be many factors at play. You can also try searching 'vibration isolators' and 'flexible ductwork connections'.

Another thing worth looking into with respect to the banging noise is whether the ductwork is too thin (perhaps less than minimum industry standards or Code?) - this is something I encountered with my own home installation.

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Date/Time2/1/2022 at 11:39:24 AM

safe and sound will help, but personally I think you have a bad install, you should not be getting "any noise" period from a brand new install, did the contractor even look at it?, get a 2nd opinion from another mechanical company

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